Animals are amazing. They often have abilities that seem as if they’ve been lifted out of some science fiction story. Game stats for animals often (usually?) give the short shrift to some of the remarkable things animals can do. For example, a tiger’s roar can stun its prey via infrasound frequencies. Check out Pathfinder‘s tiger stats. There’s no stunning sonic roar attack there (and, in my opinion, there should be).

Let’s look at snakes, since today is all about the S. Pathfinder snakes have the scent extraordinary ability, which makes sense. Snakes track prey through scent. The receptors on the snake’s tongue provide a sort of directional sense of smell and taste at range. Yes, that snake can sort of taste you without actually having to lick you. Snakes can also detect movement by picking up faint vibrations transmitted through the ground and the air. It’s not impossible to sneak up on a snake, but it isn’t that easy either. Many types of snakes — and not just pit vipers — also exhibit sensitivity to the infrared portion of the spectrum.
If I were going to feature snakes as a regular foe for my players’ characters, I’d consider beefing them up just a bit. All snakes should have a racial bonus to Perception checks and/or Skill Focus (Perception) as a feat or bonus feat. This bonus would account for the snake’s superior olfactory senses and its ability to detect vibrations. Tremorsense might seem like a good fit, but this ability is too good for the average snake since tremorsense permits the ability to automatically pinpoint a creature’s location. As mentioned above, it is possible to sneak up on a snake if one is sufficiently stealthy.

But what about that infrared sensitivity? The game doesn’t have a good equivalent. Darkvision doesn’t fit because darkvision is sort of magical. The easiest thing to do is to ignore penalties for Perception checks related to darkness that a snake would otherwise suffer so long as the snake is sensing a warm-blooded creature. (Or, in the case of creatures without blood, those that otherwise generate their own body heat, such as fire elementals, although what a snake would be doing preying on a fire elemental, I don’t know.)

Snakes also tend to be ambush predators, many of which stalk their prey. Racial bonuses to Escape Artist (to squeeze into lairs) and Stealth are appropriate. (Most snake game stats include the latter.)

When a snake constricts its prey, unconsciousness or death by asphyxiation is a real risk. The constrictor is sensitive enough to detect when its prey exhales, and it tightens its grip at that time, putting more pressure on the lungs and reducing the capacity of those organs to inhale. The rules enable a constrictor to inflict additional damage with every successful grapple check, but they don’t reflect the risk of asphyxiation.

I’d like to playtest a variation of the suffocation rules to reflect the asphyxiation hazard associated with constriction. A character being constricted has enough air to last 2 rounds per point of Constitution plus 1 additional round per point of Strength. If a character takes a standard or full-round action, the remaining air duration for the character is reduced by 1 round. Also, remaining air duration is reduced by 1 round per point of damage the character suffers due to constriction. Once a character has no more air left, he must make a DC 10 Constitution check in order to avoid suffocation. The check must be repeated each round, with the DC increasing by +1 for each previous success. When the character fails one of these Constitution checks, he begins to suffocate. In the first round, he falls unconscious (0 hit points). In the following round, he drops to –1 hit points and is dying. In the third round, he suffocates.